package com.leetcode;

import java.util.*;

/**
 * @author Dennis Li
 * @date 2020/9/7 22:32
 */
public class NotRepeat_4 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String value = sc.next();

        Set<Character> set = new LinkedHashSet<>();

        for (int i = value.length() - 1; i >= 0; i--) {
            set.add(value.charAt(i));
        }

        set.forEach(System.out::print);
    }

}
